There are many known types of RGB monitors, using various display technologies, including but not limited to cathode ray tubes (CRT), light emitting displays (LED), plasma, projection displays, liquid crystal display (LCD) devices and others. Over the past few years, the use of color LCD devices has been increasing steadily. A typical color LCD device may include a light source, an array of liquid crystal (LC) elements (cells), for example, an LC array using Thin Film Transistor (TFT) active-matrix technology, as is known in the art. The device may further include electronic circuits for driving the LC array cells, e.g., by active-matrix addressing, as is known in the art, and a tri-color filter array, e.g., a RGB filter array, registered and juxtaposed on the LC array. In existing LCD devices, each full-color pixel of the displayed image is reproduced by three sub-pixels, each sub-pixel corresponding to a different color, e.g., each pixel is reproduced by driving a respective set of R, G, and B sub-pixels. For each sub-pixel there is a corresponding cell in the LC array. Back-illumination source provides the light needed to produce the color images. The transmittance of each of the sub-pixels is controlled by the voltage applied to the corresponding LC cell, based on the RGB data input for the corresponding pixel. A controller receives the input RGB data, and adjusts the magnitude of the signal delivered to the different drivers based on the input data for each pixel. The intensity of white light provided by the back-illumination source is spatially modulated by the LC array, selectively attenuating the light for each sub-pixel according to the desired intensity of the sub-pixel. The selectively attenuated light passes through the RGB color filter array, wherein each LC cell is in registry with a corresponding color sub-pixel, producing the desired color sub-pixel combinations. The human vision system spatially integrates the light filtered through the different color sub-pixels to perceive a single integrated color image.
LCDs are used in various applications. LCDs are particularly common in portable devices, for example, the small size displays of personal digital assistant (PDA) devices, game consoles, and mobile telephones, and the medium size displays of laptop (“notebook”) computers. These applications require thin and miniaturized designs and low power consumption. LCD technology is also used in non-portable devices, generally requiring larger display sizes, for example, desktop computer displays and TV sets. Different LCD applications may require different LCD designs to achieve optimal results. The more “traditional” markets for LCD devices, e.g., the markets of battery-operated devices (e.g., PDA, cellular phones, and laptop computers) require LCDs with high brightness efficiency, which leads to reduced power consumption. In desktop computer displays, high resolution, image quality and color richness are the primary considerations, and low power consumption is only a secondary consideration. Laptop computer displays require both high resolution and low power consumption; however, picture quality and color richness are compromised in many such devices. In TV display applications, picture quality and color richness are generally the most important considerations; power consumption and high resolution are secondary considerations in such devices.
A color sequential display may create a color image by dividing the color data to fields of the colors of the display and presenting these fields sequentially in time. For example, in RGB display the color data may be divided to red data, green data, and blue data, which may be displayed individually in sequence and repeated rapidly. Color sequential displays may be activated at a sufficiently high frequency to enable a viewer to temporally integrate the sequence of primary images into a full color image. Additionally, to produce a video image, the color sequential displays may be activated at a sufficiently high rate to enable reproduction of the required number of frames per second.
A sequential color LCD device may include a light source for back-illumination and an array of liquid crystal (LC) elements (cells). For example, the LC cells may be implemented using Thin Film Transistor (TFT) active-matrix technology, as is known in the art. The device further includes electronic circuits for driving the LC array cells, e.g., by active-matrix addressing, as is known in the art. The back-illumination of an RGB display may include three types of LEDs, red, green and blue, each of which color LEDs may be operated separately in a sequential manner. The transmittance of each LC cell may be controlled by the voltage applied to the LC cell and may be synchronized with the back illumination color LEDs. The color data for controlling the transmittance of each LC cell of each pixel may include, for example, the intensity of each of the colors.
U.S. Pat. No. 7,268,757 (the “'757 patent”), the disclosure of which is incorporated herein by reference in its entirety, discloses a color LCD device for displaying a color image using at least four different colors, the device including an array of LC elements, driving circuitry adapted to receive an input corresponding to the color image and to selectively activate the LC elements of the LC array to produce an attenuation pattern corresponding to a gray-level representation of the color image, and an array of color sub-pixel filter elements juxtaposed and in registry with the array of LC elements such that each color sub-pixel filter element is in registry with one of the LC elements, wherein the array of color sub-pixel filter elements comprises at least four types of color sub-pixel filter elements, which transmit light of the at least four colors, respectively.
The '757 patent also describes a sequential color LCD device using more than three colors. In such devices, color images may be produced by sequentially back-illuminating an array of Liquid Crystal (LC) cells with light of four or more, pre-selected, colors, producing a periodic sequence of four or more, respective, color images, which are temporally integrated into a full color image by a viewer's vision system. In some embodiments, sequential back-illumination with four or more colors is produced by sequentially filtering light through four or more, respective, color filters. In other embodiments, a multi-color light source, for example, a plurality of light emitting diodes (LEDs) capable of separately producing any of the four or more colors, activated individually by color to sequentially produce the different color back-illumination. The '757 patent also describes a sequential LCD display of more than three colors using only red, green, and blue LEDs and operating LEDs of different colors simultaneously during the parts of the temporal sequence.
U.S. Pat. No. 5,724,062 (the “'062 patent”) discloses a color display having a liquid crystal pixel selectably addressable during a predetermined time period, a set of at least one red, one green, and one blue color light emitting diodes positioned adjacent the liquid crystal pixel for emitting light through the liquid crystal pixel, and means connected to the liquid crystal pixel for addressing the liquid crystal pixel a plurality of times during the predetermined time period for each color so as to provide persistence when changes in color are perceived by the human eye.